There totally are night trains, I just never knew of them. Only heard this talk on HN that they are a thing of the past in Europe, and I never looked further than that. Turns out there are night trains all over Europe, from the mediterranean sea to the arctic circle!
Taking a train through Russia is also a thing I've been thinking of doing, but then there's this wannabe-warlord situation messing up a lot of lives right now :/
Looks like Berlin-Paris (or rather, Frankfurt-Paris) is really a missing link here (pun not intended). Good to see ÖBB pick up the slack when DB won't. When the NightJet line opens next year, that sounds like a good opportunity to visit France once again.
I took the Paris-Munich sleeper a while ago, and also the London-Glasgow one. Both were great.
So much better than trekking out to the airport and dealing with the security and general hassle of planes. Plus you arrive at the destination at the right time. On a plane, you either arrive to late to do much except trek to the hotel, or you have to get up at 4am to get your plane (and still arrive around lunchtime).
However, it's generally between 2 and 5 times more expensive then a flight, so it doesn't always work out. You can do a coach too, but that is pretty uncomfortable.
I took a sleeper train several times in my life, but my experience was mostly bad. The compartment shakes too much, I was waken up by bright floodlights outside and long, loud loudspeaker messages like "Train Foo goes to Bar, composition of wagons is XYZ, regular departure at 3:00 am, current delay is 20 minutes, we apologize for the delay which was caused by C." in two languages at every stop in between.
These might be a Czech and Slovak specialty, though. Maybe western wagons do not shake as much, western curtains do really block the sharp industrial light and western stations do not pronounce such long messages at every opportunity. IDK.
Japan's night trains are, sadly, almost gone, but that's because the bullet train network now covers all the major islands. There are quite a few luxury tourist sleepers though if you're willing to fork out $1000/night or so.
Making a major resurgence in the last few years though. We took a direct Amsterdam-to-Innsbruck sleeper train earlier this year and there are several companies operating sleeper trains to other parts as well. Somewhere next month the Brussels-Amsterdam-Prague line will start and several more are in planning.
The biggest downside of sleeper trains IMO is that they are only really suitable for certain distances. It's not very nice to arrive somewhere at 02:00, so you really need a destination that is at least 8-10 hours away from your origin.
I had newly found and was exploring this concept of European night trains only last week so don't have concrete experience with planning this yet, but I did see notes in some places that you can disembark until 7am even if the train arrived at 5:something am already. If it drives only from 23:00--02:00 then I'd imagine you're out of luck indeed, but they do accommodate this problem in some cases.
